The major objective is to correlate the binding properties with the three-dimensional structures of monoclonal antibodies and their fragments. Human proteins will be isolated from the sera (IgG and IgM immunogobulins) and urines (Bence-Jones proteins) of patients with multiple myeloma, amyloidosis and Waldenstrom's macroglobulinemia. Selection of the IgM macroglobulins will be strongly biased toward those forming immune complexes with IgG antibodies (i.e., IgM rheumatoid factors). Murine monoclonal antibodies produced by hybridoma technology will include high-affinity anti-fluorescyl antibodies, a family of antifluorescyl antibodies expressing cross-reactive idiotypes to the high-affinity molecules, and anti-single stranded DNA antibodies from mice with a syndrome similar to lupus erythematosus. The patient Mcg suffered from amyloidosis and the amyloid fibrils accumulating in the tissues were presumably derived from the immunoglobulin light chain. The accumulation of protein may, in part, be attributable to the exceptioal binding properties of the Mcg light chain dimer. As crystallized in ammonium sulfate (trigonal form), the Mcg dimer has a large, malleable binding region capable of interacting with fluorescent compounds and peptides whose normal biological activities are mediated through receptors (e.g., chemotactic peptides, enkephalins and casomporphins). The detailed modes of binding of these ligands will continue to be determined by difference Fourier analysis at 2.7-A resolution, in combination with interactive computer graphics. When crystallized in deionized water (orthorhombic form), the Mcg dimer assumes a signficanctly different 3-D structure. The analysis of this structure will be extended to the limit (2.0-A) of the crystallographic data, and a comparison will be made of the trigonal and orthorhombic forms. In a parallel structural study, a hybrid of the Mcg light chain with the Weir proteins shows a marked resemblance to the 3-D structure of the Mcg dimer (trigonal form), despite 36 amino acid substitutions in the V domain of the Weir component. Models of immunoglobulin domains will be fitted to improved electron density maps for the parent Mcg IgG1 immunoglobulin, and the composite structure will be refined to convergence with the CORELS program for rigid body refinement (Hersberg and Sussmann). Structural analyses of murine Fabs will be continued by methods similar to those outlined above.